The invention relates generally to weighing and packaging systems and deals more particularly with an apparatus and process for testing a metal detector installed in a combination weighing system.
In combination and noncombination weighing systems, it is possible for a piece of metal to inadvertently appear with a product being weighed. Such a piece of metal may be a metal shaving that resulted from one moving part bearing against another part or may be a metal washer or nut that came loose as a result of vibrations within the machine. Such metal pieces are usually highly objectionable, especially if the packaged product is a food product, and it is important to prevent a contaminated package from reaching the hands of a consumer.
Heretofore, a metal detector has been installed around a discharge chute of a combination weighing machine leading into a packaging machine. Weighed quantities of product pass through the metal detector, and if a metal object is detected in the product, the metal detector is activated and signals the weighing machine to halt. Unfortunately, such metal detectors are subject to failure or may need adjustment, and as a result, it is desirable to periodically test the detector.
In the past, to perform the test, operators shut down the weighing machine and dropped a small metal object into the discharge chute and noted the response if any of the metal detector. Then the operator retrieved the metal object from a package beneath the discharge chute or discarded the package. There are a few problems with this test procedure. Production is halted during the time it takes for the operator to perform the test. Also, the test is not entirely realistic because there is little control over the initial velocity at which the operator delivers the metal object to the common discharge chute and this velocity may effect the sensitivity of the metal detector. Moreover, the metal object is not surrounded by regular product so that it travels through the common discharge chute more rapidly than would be the case if it were interspersed with a measured batch of the product.
In the past, operators have also performed a metal detection test while the machine is operating by dropping a small metal test object into the discharge chute. An additional problem has arisen in this test procedure when the metal detector is not working because under such conditions, there is no automatic means for identifying the contaminated package containing the test object. With a packaging rate of 60 to 100 bags per minute, it is often difficult for the operator to locate the contaminated package. In addition, this test procedure is not altogether realistic because the operator imparts to the metal object an initial velocity which may be different than that which it would experience if it entered the discharge chute along with the packaged product.
Accordingly, a general object of the present invention is to provide an apparatus and method for testing a metal detector in a manner which simulates actual packaging conditions.
Another object of the present invention is to provide a metal testing apparatus and method which may be utilized without interrupting weighing and packaging operations.
A more specific object is to provide an apparatus and method of the foregoing type which minimize the chance that a package contaminated with a metal test object is inadvertently transported from the weighing and packaging station for shipping to a customer.
Another specific object of the present invention is to provide an apparatus and method of the foregoing type which does not cause a filled test package to be wasted.
Still another specific object of the invention is to provide an apparatus and method of the foregoing type which fully automates the testing operation.